Hex Dump using absolute arrays and indexed pointers demo

[Michael Mattias]

' HEXDIGITS.BAS
' Demo of converting a long string of characters to hex digits using both
' an absolute array and offset pointers.
' 3/29/03
' Author: Michael Mattias Racine WI
' Public Domain
' Compiler: PB/Win 7.00

#COMPILE EXE
#DEBUG ERROR ON
#REGISTER NONE
#TOOLS OFF
#DIM ALL

FUNCTION PBMAIN() AS LONG
  CALL TestHexDigits
END FUNCTION

FUNCTION TestHexDigits() AS LONG

  LOCAL I AS LONG, FileData AS STRING, HexData AS STRING
  LOCAL pSrc AS BYTE PTR, pDest AS STRING PTR * 2, OutputBUff AS STRING


  ' build a "test file"
  FOR I = 255 TO 0 STEP -1
      FileData = FileData & CHR$(I)
  NEXT

  ' build a Table of ALL hex characters...(not just x'00' - x'0F')
  FOR I = 0 TO &hFF
      HexData = HexData & HEX$(I,2)
  NEXT

  '=================================================================
  ' METHOD ONE: Use Absolute Array
  '=================================================================
  ' define an array of 2 character strings overlaying our hex
  ' characters table:
  REDIM HexChar(&hFF) AS STRING * 2 AT STRPTR(HexData)
 ' Build an output buffer: 2 hex chars required per input character:
  OutputBuff             =  SPACE$(LEN(FileData)*2)
  pSrc                   =  STRPTR (FileData)     ' point to start of input
  pDest                  =  STRPTR (OutputBuff)   ' and output

  FOR I = 1 TO LEN(FileData)          ' for each byte of input
     @pDest   =  HexChar(@pSrc)       ' move 2 hex characters to output
     INCR  pSrc                       ' and advance in input & output
     INCR  pDest
  NEXT
  ' show the output, should be 512 characters x'FF'- x'00'
  MSGBOX OutputBuff,, "Using ARRAY"

  '=================================================================
  '    METHOD TWO: Use Offset Pointers
  '=================================================================

  LOCAL      pHex AS STRING PTR * 2

  OutputBuff = SPACE$(LEN(FileData)* 2)    ' reset the output
  pSrc        =  STRPTR (FileData)         ' point to start of input
  pDest       =  STRPTR (OutputBuff)       ' and output
  pHex        =  STRPTR (HexData)          ' set base of lookup table
  FOR I = 1 TO LEN(FileData)               ' for each byte of input
     @pDest   =  @pHex[@pSrc]              ' move 2 hex characters to output
     INCR  pSrc                            ' and advance in input & output
     INCR  pDest
  NEXT
 ' show the output, should be 512 characters x'FF' - x'00'
  MSGBOX OutputBuff, ,"Using Offset pointers"


END FUNCTION

------------------
Michael Mattias
Tal Systems Inc.
Racine WI USA
mailto:[email protected][email protected]</A>
www.talsystems.com

[Michael Mattias]

And to go the other way.... from hex pairs to a byte stream....

ie., every two characters of input represents a hex pair; each output character = CHR$(VAL(Hex pair))

#COMPILE EXE
#DIM ALL
#COMPILER PBWIN 8.03

FUNCTION PBMAIN () AS LONG
 LOCAL wIn AS STRING, WOut AS STRING
 LOCAL i AS LONG, TestOut AS STRING
 
 wIn =  "01234567890ABCDEF01234567890ABCDEF"  ' <<< "THE JPEG"
 wOut = ""
  
 CALL HexPairsToCharString (wIn, Wout)
  
  ' test return and show results...
  FOR I = 1 TO LEN(Wout)   ' for each character of output
      Testout = Testout & HEX$(ASC(wOut,I),2)
  NEXT
  MSGBOX  "In ="  & wIn & $CRLF & "Out=" & TEstOut

END FUNCTION


SUB HexPairsToCharString( sBuf AS STRING, Work AS STRING)
 LOCAL i AS LONG, pSrc AS BYTE PTR, pDest AS BYTE PTR
 LOCAL nibble AS BYTE, iLen AS LONG
    
    '---------------------------------------------------------------
    ' make destination string, will be one-half the length of input
    '---------------------------------------------------------------
    iLen  = LEN (sBuf)
    Work  = STRING$(ilen\2, 0 )   ' string of CHR$(0)
    
    pSrc  = STRPTR (sBuf)         ' point at first chars of input and output
    pDest = STRPTR (Work)
    
    FOR I = 1 TO iLen             ' for each character of input
        SELECT CASE AS LONG @pSrc
            CASE &h30? TO &h39?        ' digits zero to nine
                nibble           =  @pSrc - &h30?     ' convert from display to decimal values 0-9
            CASE &h41? TO &h46?            ' digits "A" thur "F"
                nibble           =  @psrc - &h37?     ' convert from display to decimal values 10-15
       END SELECT
       IF I MOD 2 THEN             ' working on high-order nibble
            @pDest   = nibble      ' store
            SHIFT LEFT @pdest, 4   ' move to high order position
       ELSE
           @pdest  = @pDest OR nibble  ' add nibble value to low-order position, preserving high order
           INCR      pDest             ' done with this output char, advance to next
       END IF
       INCR pSrc  ' advance to next input char
    NEXT I
    
END SUB

[This message has been edited by Michael Mattias (edited August 19, 2007).]